The invention relates to an elastomer member with non-tacky surface treating layer and a method of manufacturing the same, and more particularly, to an elastomer member which may be used as a transfer, a developing or a conveyor roller or belt in an electrophotographic copying system and which is provided with a non-tacky surface treating layer in order to prevent contamination thereof as a result of the deposition of toner thereon, and a method of manufacturing the same.
As is well recognized, an electrophotographic copying system utilizes a variety of elastomer members acting as conveyor rollers or belts for a sheet carrying an unfixed toner image thereon, transfer roller or belt which urges a sheet in superimposed relationship with a toner image to effect a transfer of the toner image, and developing roller or belt as may be used in an impression developing unit (see U.S. Pat. Nos. 3,731,146 and 3,754,963). Considering a roller, by way of example, a conventional elastomer member of the kind described generally comprises a core metal which is surrounded by a layer of material, or elastomer, having a rubber-like elasticity under normal temperatures.
When these elastomer rollers are utilized as conveyor, transfer and developing rollers where they are subject to contamination by toner, the deposition of the toner onto the roller surface causes the sheet to be marred by toner.
To avoid this problem, there has been proposed a technique whereby a surface treating layer of a material which is different from the material forming the elastomer layer is deposited on the surface of the elastomer roller.
In one technique, a roller which is intended to be used in the transfer of a toner image is subject to a surface treatment with a material of the similar kind as that used to form the elastomer layer in order to prevent the deposition of toner on the roller and the ionization of the atmosphere surrounding the roller. According to this technique, the elastomer layer comprises polyurethane elastomer to which a treating agent which adjusts the resistivity is added, and an elastic polyurethane having an increased resistivity is coated over the surface of the elastomer layer to a thickness of about six microns to provide a surface treating layer. Since the surface treating layer comprises an elastic material, there is no likelihood that cracks will be developed in the surface treating layer, and the formation of the surface treating layer and the inner elastomer layer of materials of a same character achieves a good bond between the both layers.
However, the inner elastomer layer may be formed from a variety of materials, and it is not assured that the surface treating layer can be formed of a material of the same character as the inner elastomer layer. Where a different material is used to form the surface treating layer, problems arise in respect to the occurrence of cracks or the insufficient bonding strength. In addition, the use of a usual material to form the surface treating layer cannot satisfactorily prevent the deposition of toner.
Another technique has then been proposed to utilize fluorocarbon polymers such as polytetrafluoroethylene (hereafter referred to as "PTFE") to form the surface treating layer in consideration of the non-tackiness of the fluorocarbon polymers.
FIG. 1 shows one form of conventional elastomer roller having a non-tacky surface treating layer on its surface. The roller shown comprises a solid cylindrical core metal 1 having a pair of support shafts 1a integrally formed on its opposite ends (only one shaft 1a is shown), an inner elastomer layer 2 disposed in surrounding relationship with the core metal 1, and a non-tacky surface treating layer 3 which is applied to the peripheral surface of the elastomer layer 2. The inner elastomer layer 2 may be formed of materials such as polyurethane elastomer, nitryl rubber, butyl rubber, chloroprene rubber, natural rubber and the like, which may be used either along or blended with a variety of additives such as a resistivity controlling agent. The non-tacky surface treating layer 3 is formed of a fluorocarbon polymer such as PTFE.
A fluorocarbon polymer such as PTFE does not dissolve in an organic solvent, and hence the surface treating layer 3 cannot be formed by coating the inner elastomer layer with a solution of fluorocarbon polymer. The material which forms the inner elastomer layer 2 generally has a reduced resistance to heat, and this prevents the fluorocarbon polymer such as PTFE from being directly applied thereto by baking. Accordingly, in order to form the surface treating layer 3 by a low temperature treatment, powder of the fluorocarbon polymer such as PTFE is suspended in a solution of binder resin, and the suspension is applied to the surface of the layer 2. The binder resin may comprise polymethyl methacrylate, cellulose, phenol, polyester polyimide or the like. The surface treating layer 3 thus applied and including the fluorocarbon polymer is converted into a hardened film:
(a) by evaporating the solvent under normal temperature to form a hardened film, or PA1 (b) by heating it to a low temperature on the order of 120.degree. to 150.degree. C. to cause a polymerizaton and hardening of the binder resin.
The hardened film formed to provide the surface treating layer 3 according to the process (a) has a degraded resistance to organic solvents, and can be easily dissolved as its surface is cleaned with an organic solvent of a reduced dissolving power such as trichlorotrifluoroethane. On the other hand, the hardened film obtained by the process (b) results in an increased film thickness which is liable to produce cracks therein. In addition, when such film is deformed by the application of an external force, the surface treating layer 3 cannot closely follow the deformation of the inner elastomer layer 2, disadvantageously resulting in an exfoliation.